1. Field of the Invention
The present invention is directed to a gas engine with electronically controlled and/or regulated ignition oil injection.
2. Description of Related Art
Internal combustion engines which are operated only or primarily with gaseous fuels are referred to as gas engines. Gas engines include, on the one hand, known Otto gas engines with electric ignition and, on the other hand, gas engines referred to as pilot-ignition gas engines or ignition oil gas engines in which ignition of the fuel-air mixture is achieved by the auto-ignition of a small quantity of injected liquid ignition oil. The principle of injection of an auto-ignition oil is also applied in dual-fuel engines or diesel/gas engines, for example, as disclosed in German Patent publication 40 33 843 A1.
Depending on its application profile, pilot-ignition gas engines or diesel/gas engines may be constructed with two different combustion processes which are known from diesel engines. These diesel engine combustion processes are classified based on the construction of the combustion chamber. On the one hand, diesel engines constructed with an undivided combustion chamber are known as direct injectors. On the other hand, chamber engines are constructed with a divided combustion chamber whereby the overall combustion chamber is divided into two individual combustion chambers by a more or less sharply narrowed orifice. That portion of the combustion chamber which includes the one defining wall formed by the piston is referred to as the main combustion chamber and the other portion of the combustion chamber is the precombustion chamber. Depending on the construction of the precombustion chamber, the engine is referred to either as a precombustion chamber engine or a swirl combustion chamber engine. In diesel engines with a divided combustion chamber, diesel fuel is injected into the precombustion chamber. In a similar manner, a pilot-injection gas engine or diesel/gas engine may be constructed as a direct injector or as a chamber engine, depending on whether the ignition oil is injected directly into the main combustion chamber or into the precombustion chamber respectively.
If the ignition oil is injected into the precombustion chamber, a fuel-air mixture with a relatively large amount of excess air may be ignited very uniformly and precisely in the main combustion chamber thereby desirably producing only a relatively small amount of harmful emissions and achieving a relatively high engine efficiency. Thus, if a low-pollutant, environmentally sound energy conversion is preeminent, the preferred construction is injection of the ignition oil into the precombustion chamber. In addition, for purely diesel operation of a diesel/gas engine, the main fuel quantity is preferably injected directly into the precombustion chamber.
In view of increasingly stringent emission controls, e.g., as defined by German technical guidelines governing air quality, for industrial installations, power plants, pumping stations and compressor plants, the reduction in the amount of pollutant of nitrogen oxides NO.sub.x is an increasingly prominent factor in engine development.
In gas engines in which the fuel-air mixture is ignited by the injection of an auto-igniting ignition oil, NO.sub.x emission standards may be maintained in gas operation without the need for catalytic aftertreatment of the exhaust only by injecting the smallest possible amount of ignition oil which would still allow for reliable ignition of the fuel-air mixture.
Various methods are already known for providing small quantities of ignition oil. For example, the ignition oil injection valve may be controlled by the main injection pump in conjunction with a metering valve for the ignition oil quantity, as for example disclosed in U.S. Pat. No. 5,297,520. Injection devices with dual nozzles are also known. Alternatively, in a known manner, a separate injection pump may be provided for ignition oil injection in addition to the main injection pump for main injection. A joint camshaft may be used as the driving means for the main injection pump and the ignition oil injection pump, or alternatively, separate camshafts may be provided.
These known solutions for controlling ignition oil injection have limited flexibility in controlling the quantity of ignition oil, selecting the injection pressure, adjusting the beginning of delivery the realization of which is very complicated and adjusting the beginning of ignition oil injection. Thus, consistently reliable metering of the quantity of ignition oil is not ensured.
For the reasons stated above ignition oil quantities less than or equal to approximately 1% of the diesel consumption at full load are desirable, however, with such low ignition oil quantities the disadvantages of the known solutions must be avoided in order to meet efficiency, emissions and operating reliability demands.
Management or control systems are known in automobile engine design, especially in Otto engines, for setting adjustment variables such as the ignition angle, injection timing and throttle position depending on the load point. For example, German Patent publication 43 26 949 A1 discloses a method for deriving a load variable from measured cylinder pressure signals for characterizing the load point and using these load variables together with the respective engine speed to determine the optimum ignition angle by means of a characteristic diagram input in the engine control computer.
It has been recognized in connection with diesel engines that it is very important to have the greatest possible flexibility in the injection system. Thus, different electronically controlled injection systems have been developed. One such system is the pump-nozzle system which is advantageous in that it produces relatively high injection pressures and reduces the dynamic effects in the hydraulic lines. However, in this system the injection pressure is disadvantageously dependent on the speed of the engine.
Other injection systems, known collectively as common rail systems, provide a freely selectable injection pressure at all engine operating points. These systems may be roughly classified depending on the fuel pressure in the common fuel line of the cylinders. In one group of common rail systems, the pressure in the common fuel line is equal to the injection pressure (high-pressure common rail), whereas in the second group the pressure in the common fuel line is substantially lower than the injection pressure (low-pressure common rail). In this second group, hydraulic pressure intensifiers comprising part of the injection device increase the low pressure from the rail to the necessary high pressure required for injection. In both cases, a hydraulic delivery pump (hydraulic pump) produces the required diesel fuel pressure in the common fuel line of the cylinders, that is, high pressure in the case of the high-pressure common rail and low-pressure in the case of low-pressure common rail. A pressure accumulator is generally disposed between the hydraulic pump and the injection device in order to reduce the dynamic effects in the pressure lines. Thus, the injection pressure is independent of the injection quantity and engine speed. The injection process may be initiated electrically and the nozzle needle may be actuated by an independent electronic control. Design and construction of the injection device varies depending on the type of common rail and also within each rail group. In these common rail systems, the pressure at the injection nozzle is approximately constant during the injection process.
It is the object of the present invention, therefore, to provide a gas engine with electronically controlled and/or regulated injection of relatively small quantities of ignition oil in such a way that the accuracy with which the quantity of injected ignition oil is metered, the flexibility in providing the quantity of ignition oil required, and the ability to optionally preset the time point of ignition oil injection are improved while maintaining NO.sub.x emission standards in gas operation without the need for catalytic aftertreatment of the exhaust.